Electron capture phenomena in proton-atom and proton-molecule collisions

Electron capture of protons, in a wide energy range, has been investigated both experimentally and theoretically by many investigators using atomic and molecular targets. Agreement between theory and experiment is very good to excellent, for cases involving atomic targets. We have observed that the additivity principle, that the electron capture cross section from the molecule is the sum of the contributions from the atomic constituents of the molecule, is violated. We have developed a reasonable model to explain the breakdown, which also yielded the ''atomic'' capture cross sections. In a very recent work, further support for the molecular dependence of the cross sections have also been provided. (orig.)